This invention relates to a sound synthesizing method and apparatus for producing synthesized sounds having a property similar to the property of natural sounds such as human voices, instrumental sounds, or the like.
Sound synthesizers have been employed for producing synthesized sounds having a property similar to the property of natural sounds such as human voices, instrumental sounds, or the like. Technological advances particularly in large scale integrated circuit (LSI) techniques have permitted the production of inexpensive sound synthesizers. In cooperation with such technological advances, various sound synthesizing techniques, such as a recording/editing technique and a parameter extraction technique, have been developed to improve the fidelity of the synthesized sounds. The recording/editing technique records various human voices and edits the recorded human voices to form a desired sentence. The parameter extraction technique extracts parameters from human voices and adjusts the extracted parameters during a sound synthesizing process to form an artifical audio signal. The parameter extraction technique includes a parcol technique which can form an audio signal with high fidelity.
It is the common practice to process a sound wave by employing a digital computer which samples the sound wave at uniform time intervals, converts the sampled values into digital form, and stores the converted digital values into a computer memory. In order to produce a synthesized sound with high fidelity, it is required to sample the sound wave at fine time intervals and increase the computer memory capacity.
Various coding techniques have been developed to reduce the memory capacity required in producing synthesized sounds. For example, a digital modulation coding technique has been employed which codes a sound wave by assigning a binary number "1" to the newly sampled value when the next value is estimated as being greater than the new value and assigning a binary value "0" to the newly sampled value when the next value is estimated as being smaller than the new value. Such a technique is called as an estimated coding and includes a linear estimating technique which makes an estimation based on the several previously sampled values and a parcor technique which utilizes a parcor coefficient rather than the estimation coefficient used in the linear estimation technique.
With such an estimation coding technique, however, a serious problem occurs in coupling successive synthesized sounds. For example, when a vowel sound, a consonant sound and a vowel sound are produced in this order, an interruption occurs between the vowel sounds to produce an unnatural or artificial impression on a person. A similar problem occurs when instrumental sounds are synthesized artifically.